Interface Control And Mechanical Behavior Of Al₁₈B₄O₃₃w Reforced Al-Mg And Al-Cu Composites

In view of the problems about the serve interfacial reaction and the low mechanical property in aluminum matrix composites reinforced by aluminum borate whisker, preparation the coating of Al2O3 on the reinforcement by the hydrothermal synthesis method and the use of alloying etc. were proposed to restrain the interfacial reaction, adjusted the interface condition and raised the interface bonding strength for increasing the mechanical property of the composite. Al2O3-coated and uncoated Al18B4O33 whiskers reinforced Al-Mg and Al-Cu matrix composites were fabricated by squeeze casting, and then heat treatment were performed on them.XRD results showed that the precursor obtained was composed of Al O（OH） after coating by the hydrothermal synthesis. The Al O（OH） phase disappeared and the new phaseγ-Al2O3 formed after calcinationn at 900℃ for 1 hour. DSC-TG results demonstrated that the Al O（OH） phase decomposed at 482℃.It was found that Mg contents influenced the interface structure of Al₁₈B₄O₃₃w/Al-Mg matrix composites notably. The reaction products evolved gradually from Mg Al2O4 phase to Mg Al2O4 and Mg O as well as Mg O with Mg content increasing. The mechanical property of the composite declined dramatically due to the damage of the whisker when the Mg contents was low. The interfacial condition improved and the mechanical property increased with the increase of Mg contents. The tensile strength of the composite reached the maximum（540MPa） as the Mg content was 10%.The existence of Al2O3 coating on the whisker surface decreased effectively the interface reaction between the whisker and Mg in the matrix of the composite, and varied the interfacial microstructure of the composite. The interracial phases were composed of Mg O and Mg Al2O4 in ABOw/Al-Mg matrix composites as Mg content reached 6.8%, and there was only Mg O phase in ABOw/Al O/Al-Mg composite. Moreover, the content of Al2O3 coating had the significant effect on the mechanical property of the composite. With the content of the Al2O3 coating increasing, the UTS and δ of the composite first increased and then declined. The UTS of ABOw/Al-Mg composite was 490 MPa as the content of Al2O3 coating reached 1.36%.Heat treatment could affect the microstructure and the mechanical property obviously. Heat treatment had no influence on the interface structure of ABOw/Al-Mg matrix composites, however, which affected those of ABOw/Al O/Al-Mg composite. The new Mg Al2O4 phase produced at the interface of ABOw/Al O/Al-Mg composite owing to the reaction between Al2O3 coating and Mg in the matrix.It was found that no reactions happened at the interface between ABOw and the matrix in Al-Cu matrix composite, but there were Cu Al2 phase precipitated in the matrix or at the interface. The size and the amount of the Cu Al2 phase at the interface increased in Al-Cu matrix composite with the increase of Cu content. The coating on the whisker surface varied the distribution of the second phase at the interface and in the matrix. Cu Al2 phases only aggregate at the interface in as-cast ABOw/Al-Cu matrix composites, and they were not precipitated in the matrix. However, Cu Al2 phases not only precipitated at the interface but also in the matrix in as-cast at this time, there existed the regions without the precipitation at the interface between the whisker and the matrix. The redissolution occurred to the coarse second phased after solution treatment, which caused the size of the second phase to decrease and Cu Al2 phase to precipitate in the matrix. While, heat treatment made the size of the second phase reduce at the interface in ABOw/Al O/Al–Cu composites, and the second phase grew up in the matrix.The UTS varied little and the δ decreased markedly in as-cast ABOw/Al-Cu composite with the increase of Cu content. For as-cast ABOw/Al O/Al-Cu composites, the coating increased the brittleness of the interface, and worsened interface state, leading to the UTS and the ductility being lower than those of ABOw/Al-Cu composite significantly. In addition, the coating also affected the aging behavior of Al-Cu matrix composite. The UTS obtained the maximum value 565 MPa after 3.5h aging treatment in ABOw/Al-Cu composite. As to ABOw/Al O/Al-Cu composites, the UTS reached the maximum after solution treatment and the UTS and the ductility all decreased after aging.